Carbon electrode kinetics

Bourdillon, C., Bourgeois, J. B., Thomas, D., Covalent Linkage of Glucose Oxidase on Modified Glassy Carbon Electrodes. Kinetic Phenomena , J. Am. Chem. Soc. 102 (1980) 4231-4235. 

Mashkina, E. and Bond, A.M. (2011) Implementation of a statistically supported heuristic approach to alternating current voltammetric harmonic component analysis re-evaluation of the macrodisk glassy carbon electrode kinetics for oxidation of ferrocene in acetonitrile. Analytical Chemistry, 83,1791-1799. 

Kinetic stability of lithium and the lithiated carbons results from film formation which yields protective layers on lithium or on the surfaces of carbonaceous materials, able to conduct lithium ions and to prevent the electrolyte from continuously being reduced film formation at the Li/PC interphase by the reductive decomposition of PC or EC/DMC yielding alkyl-carbonates passivates lithium, in contrast to the situation with DEC where lithium is dissolved to form lithium ethylcarbonate [149]. EMC is superior to DMC as a single solvent, due to better surface film properties at the carbon electrode [151]. However, the quality of films can be increased further by using the mixed solvent EMC/EC, in contrast to the recently proposed solvent methyl propyl carbonate (MPC) which may be used as a single sol-... 

R.L. McCreery, Carbon Electrodes Structural Effects on Electron Transfer Kinetics, in A.J. Bard, Ed., Electroanalytical Chemistry, Vol 18, Marcel Dekker, New York, 1991. 

Fhosphoric acid does not have all the properties of an ideal fuel cell electrolyte. Because it is chemically stable, relatively nonvolatile at temperatures above 200 C, and rejects carbon dioxide, it is useful in electric utility fuel cell power plants that use fuel cell waste heat to raise steam for reforming natural gas and liquid fuels. Although phosphoric acid is the only common acid combining the above properties, it does exhibit a deleterious effect on air electrode kinetics when compared with other electrolytes ( ) including such materials as sulfuric and perchloric acids, whose chemical instability at T > 120 C render them unsuitable for utility fuel cell use. In the second part of this paper, we will review progress towards the development of new acid electrolytes for fuel cells. 

Great promise exists in the use of graphitic carbons in the electrochemical synthesis of hydrogen peroxide [reaction (15.21)] and in the electrochemical reduction of carbon dioxide to various organic products. Considering the diversity in structures and surface forms of carbonaceous materials, it is difficult to formulate generalizations as to the influence of their chemical and electron structure on the kinetics and mechanism of electrochemical reactions occurring at carbon electrodes. 

Gonzalez-Garcia J, Gallud F, Iniesta J et al (2001) Kinetics of electrocrystallization of Pb02 on glassy carbon electrodes influence of ultrasound. New J Chem 25 1195-1198... 

One final issue remains to be resolved Of the portion of the AEpi that is due to resistance, what part is caused by solution resistance and what part is caused by film resistance To explore this issue we examined the electrochemistry of a reversible redox couple (ferrocene/ferricinium) at a polished glassy carbon electrode in the electrolyte used for the TiS 2 electrochemistry. At a peak current density essentially identical to the peak current density for the thin film electrode in Fig. 27 (0.5 mV see ), this reversible redox couple showed a AEpi of 0.32 V (without application of positive feedback). Since this is a reversible couple (no contribution to the peak separation due to slow kinetics) and since there is no film on the electrode (no contribution to the peak separation due to film resistance), the largest portion of this 0.32 V is due to solution resistance. However, the reversible peak separation for a diffusional one-electron redox process is —0.06 V. This analysis indicates that we can anticipate a contribution of 0.32 V -0.06 V = 0.26 V from solution resistance in the 0.5 mV sec control TiS2 voltammogram in Fig. 27. 

In general, the electrochemical performance of carbon materials is basically determined by the electronic properties, and given its interfacial character, by the surface structure and surface chemistry (i.e. surface terminal functional groups or adsorption processes) [1,2]. Such features will affect the electrode kinetics, potential limits, background currents and the interaction with molecules in solution [2]. From the point of view of electroanalysis, the remarkable benefits of CNT-modified electrodes have been widely praised, including low detection limits, increased sensitivity, decreased overpotentials and resistance to surface fouling [5, 9, 11, 17]. 

The electronic properties of CNTs, and especially their band structure, in terms of DOS, is very important for the interfacial electron transfer between a redox system in solution and the carbon electrode. There should be a correlation between the density of electronic states and electron-transfer reactivity. As expected, the electron-transfer kinetics is faster when there is a high density of electronic states with energy values in the range of donor and acceptor levels in the redox system [2]. Conventional metals (Pt, Au, etc.) have a large DOS in the electrochemical potential... 

To summarize, one can say that the electrochemical performance of CNT electrodes is correlated to the DOS of the CNT electrode with energies close to the redox formal potential of the solution species. The electron transfer and adsorption reactivity of CNT electrodes is remarkably dependent on the density of edge sites/defects that are the more reactive sites for that process, increasing considerably the electron-transfer rate. Additionally, surface oxygen functionalities can exert a big influence on the electrode kinetics. However, not all redox systems respond in the same way to the surface characteristics or can have electrocatalytical activity. This is very dependent on their own redox mechanism. Moreover, the high surface area and the nanometer size are the key factors in the electrochemical performance of the carbon nanotubes. 

The electroreduction of some typically inorganic compoimds such as nitrogen oxides is catalysed by the presence of polymeric osmium complexes such as [Os(bipy)2(PVP)2oCl]Cl, where bipy denotes 2,2 -bipyridyl and PVP poly(4-vinylpyridine). This polymer modifies the reduction kinetics of nitrite relative to the reaction at a bare carbon electrode, and provides calibration graphs of slope 0.197 nA with detection limits of 0.1 pg/mL and excellent short-term reproducibility (RSD = 2.15% for n = 20). The sensor performance was found to scarcely change after 3 weeks of use in a flow system into which 240 standards and 30 meat extracts were injected [195]. 

The voltammetric reduction of a series of dialkyl and arylalkyl disulfides has recently been studied in detail, in DMF/0.1 M TBAP at the glassy carbon electrode The ET kinetics was analyzed after addition of 1 equivalent of acetic acid to avoid father-son reactions, such as self-protonation or nucleophilic attack on the starting disulfide by the most reactive RS anion. Father-son reactions have the consequence of lowering the electron consumption from the expected two-electron stoichiometry. Addition of a suitable acid results in the protonation of active nucleophiles or bases. The peak potentials for the irreversible voltammetric reduction of disulfides are strongly dependent on the nature of the groups bonded to the sulfur atoms. Table 11 summarizes some relevant electrochemical data. These results indicate that the initial ET controls the electrode kinetics. In addition, the decrease of the normalized peak current and the corresponding increase of the peak width when v increases, point to a potential dependence of a, as discussed thoroughly in Section 2. 

Electrode Kinetics and Electrocatalysis in Molten Carbonate Fuel Cells... 

An electrocatalytic reaction is an electrode reaction sensitive to the properties of the electrode surface. An electrocatalyst participates in promoting or suppressing an electrode reaction or reaction path without itself being transformed. For example, oxygen reduction electrode kinetics are enhanced by some five orders of magnitude from iron to platinum in alkaline solutions or from bare carbon to carbon electrodes modified with Fe phthalocyanines or phenylporphyrins. For a comprehensive discussion of the subject, the reader is referred to refs. (76, 95, and 132-136). 

In the previous edition of this book, Dryhurst and McAllister described carbon electrodes in common use at the time, with particular emphasis on fabrication and potential limits [1]. There have been two extensive reviews since the previous edition, one emphasizing electrode kinetics at carbon [2] and one on more general physical and electrochemical properties [3]. In addition to greater popularity of carbon as an electrode, the major developments since 1984 have been an improved understanding of surface properties and structure, and extensive efforts on chemical modification. In the context of electroanalytical applications, the current chapter stresses the relationship between surface structure and reproducibility, plus the variety of carbon materials and pretreatments. Since the intent of the chapter is to guide the reader in using commonly available materials and procedures, many interesting but less common approaches from the literature are not addressed. A particularly active area that is not discussed is the wide variety of carbon electrodes with chemically modified surfaces. 

The primary objective of the discussion that follows is to establish a basis for choosing and applying carbon electrodes for analytical applications. As with any electrode material or electroanalytical technique, the choice depends on the application there is no ideal electrode for all situations. We first discuss the criteria that drive the chemist s choice of electrode or procedure. These criteria include background current, potential limits, and electrode kinetics, and may be considered dependent variables that are ultimately controlled by the properties of the carbon surface. Then we consider the independent variables that determine electroanalytical behavior. These include the choice of carbon material, surface roughness, cleanliness, etc. By considering the dependence of electroanalytical behavior on surface variables that the user can control, it should be possible to make rational choices of electrodes and procedures to lead to the desired analytical objective. 

Before discussing particular carbon electrode materials, we should define the qualities on which a choice of material will be based. These are the criteria that matter the most to the user, and the importance of each will vary with the application. For example, a carbon electrode to be used for detecting eluents from a liquid chromatograph should have a low background current and long stability, whereas an electrode used for studying redox mechanisms should usually exhibit fast electron transfer kinetics. The criteria relevant to carbon electrodes are conveniently classified into four types. 

Carbon electrodes exhibit a wide range of electron transfer rates for benchmark redox systems, depending on carbon material and surface history. Two examples are shown in Figure 10.2, which compares two carbon surfaces with very different k° for Fe(CN) /4. In some cases, the variations in electrode kinetics have been particularly important to analytical applications. For example, carbon paste and carbon fiber electrodes have been used to monitor neurotransmitters in living animal brains [5,6]. The determination of catechol transmitters in the presence of relatively large amounts of interferents (e.g., ascorbate) de-... 

---